1. Field of the Invention
The present invention relates to a light source unit and a projector which includes the light source unit.
2. Description of the Related Art
In these days, data projectors are used on many occasions as image projection apparatuses which project images including images of screens and video images of personal computers, as well as images based on image data which is stored in memory cards on to a screen. These projectors are such that light emitted from a light source is collected to a micromirror device called DMD (Digital Micromirror Device) or a liquid crystal plate for display of a color image onto the screen.
In projectors of the type described above, conventionally, projectors using a high-intensity discharge lamp as a light source have been the mainstream of projectors. However, when a white discharge lamp is used as a light source, the color of light from the light source is divided by a color wheel including red, green and blue color filters to cut off other light than light to be used, leading to a problem that the utilization efficiency of light from the light source is low. To cope with this problem, in recent years, there have been made many developments on projectors which use, as a light source, a light emitting diode, a laser diode, a device utilizing organic EL technology or luminescent materials.
For example, Japanese Unexamined Patent Publication No. 2004-341105 (JP-A-2004-341105) proposes a light source unit having a light emitting diode as an excitation light source and a luminescent wheel in which a luminescent material layer or layers which convert ultraviolet light emitted from the excitation light source into visible light are formed on a transparent base material.
Japanese Unexamined Patent Publication No. 2003-295319 (JP-A-2003-295319) proposes a single-color light source unit in which laser beams from laser diodes functioning as excitation light sources are shone on to luminescent materials so that luminescent light rays emitted from the luminescent materials are emitted as parallel light rays by a reflector.
The proposal made in JP-A-2004-341105 is configured so that light rays of red, green and blue wavelength bands can be emitted sequentially. However, since excitation light needs to be shone individually onto the luminescent light emitting areas of the respective colors formed on a surface of the luminescent wheel, there is caused a problem that a large load has to be borne by the excitation light source which is driven at all times. Because of this, the drive output of the excitation light source needs to be suppressed to as to suppress the increase in temperature thereof. In addition, since the colored luminescent light rays are designed to be emitted sequentially from the corresponding luminescent light emitting areas which are formed on the luminescent wheel which rotates at a predetermined rotating speed, periods of time when the colored light rays are emitted from the respective luminescent light emitting areas are restricted by a ratio of the luminescent light emitting areas of the respective colors which are formed on the luminescent wheel. Thus, in the event that a period of time when the light ray of the specific wavelength band is attempted to be lengthened, there is no other way but to adjust it by shortening the periods of time when the light rays of the other wavelength bands are emitted, leading to a problem that the utilization efficiency of light is reduced.
Additionally, the emission of colored light rays from the corresponding luminescent light emitting areas largely depends on the physical properties of the luminescent materials, and therefore, there is also caused a problem that it becomes difficult to display an image with a superior color balance on the screen.
The light source unit can be configured as a light source unit which has a plurality of types of semiconductor light emitting devices so that all the light rays of respective colors can be produced by light emitting diodes. However, as this occurs, there is a situation in which for example, a green semiconductor light emitting device has difficulty in obtaining a higher intensity than those of the other red and blue semiconductor light emitting devices.
The single-color light source unit proposed in JP-A-2003-295319 can be configured so as to project a color image onto the screen by disposing three single-color light source units which function as red, green and blue light source units in the projector. However, since the luminescent materials which receive the citation laser beams to emit the light rays of predetermined wavelength bands are fixed so as not to move, the shining positions of the excitation laser beams are not changed, and hence, the temperatures of the luminescent materials are increased, whereby there is caused a problem that a reduction in wavelength converting efficiency and a deterioration in performance with time are generated by the increase in the temperatures of the luminescent materials.
Here, the respective single-color light source units can be configured with luminescent wheels each. However, as this occurs, excitation light from an excitation light shining device which is controlled with time sharing is shone onto various portions on luminescent material layers which are laid circumferentially on the luminescent wheel. Namely, the shining positions of excitation light on the luminescent material layers scatter thereon, causing portions onto which the excitation light is shone repeatedly and portions onto which almost no excitation light is shone. This promotes the deterioration of only the portions of the luminescent material layers, whereby a reduction in light emission efficiency of the portions in question is called for, inducing an image displayed on the screen to flicker.